Condensation of magnesium vapor



Aug. 12, 1941. J. D. HANAWALT.

CONDENSATION OF MAGNESIUM VAPOR Filed Jan. 29, 1940 r/ 0 Z m 2 fi T 5 Hj W a ODD DDDDQ" m K {W 3% 1w 5 A e w n, v r? Occcoooc w ATTORNEYSPatented Aug. 12, 1941 CONDENSATION 0F MAGNESIUM VAPOR Joseph- D.Hanawalt, Midiand, Michr, assignor to The Dow Chemical Company, Mi

dhnd, Mich,

a corporation of Michigan Application January 29, 1940, Serial No.316,199

SCIaims.

The invention relates to an improved method of condensing magnesiumvapor.

The condensation of magnesium vapor to recover the metal substantiallyall in liquid form involves a number of serious practical diiiiculties,

all resulting from the fact that liquid magnesium dust, even ifcollected, cannot satisfactorily be melted down, but must be convertedto massive magnesium by expensive methods.

An object of the present invention is to provide an improved method ofcondensing magnesium vapor. Another object isto provide a method inwhich the metal is substantially all converted into liquid form, eventhough the vapor is supplied under such conditions that the vaporpressure of the condensed liquid magnesium is an appreciable fraction ofthe partial pressure of the magnesium vapor.

According to the invention, magnesium vapor to be condensed is passedsuccessively into two condensing zones, which are maintained attemperatures respectively above and below the melting point ofmagnesium. In the first zone most of the vapor is condensed to liquidmagnesium, and in the second zone the remaining vapor is condensed tosolid magnesium, usually in powder form. All the magnesium condensed isrecoverable. If desired, condensate from the second zone may be returnedinto contact with the liquid condensate in the first zone where it meltsand coalesces with the main body of condensed magnesium. In this way,substantially all the vapor condensed in both zones is finally obtainedin the liquid state. i

The invention may be explained in detail with reference to theaccompanying drawing, in

which:

Figure l is a vertic one form of appar view, partly in section, ofadapted to carrying out th process of the invention; and

Figure 2 is a similar view of another form of apparatus.

The magnesium condenser. shown in Figure 1 consists of a verticalelongated metal cylinder ii provided with a vapor inlet l2 near itslower end and terminated at the bottom by a closed reservoir it, whichmay be heated by an electric resistance element i4, and from whichliquid metal can be withdrawn through double valves It and it with anintermediate receiver ii. The apparatus is closed at the top by a coverll provided with a gas outlet is. The condenser ii is divided into alower zone A and an upper zone B which are cooled by radiation, and maybe heated, if desired, by independent electric re- In operation, thereservoir i3 and the lower condensing zone A are raised to a temperatureslightly above the melting point of magnesium by passing electriccurrents of suitable magnitime through their respective resistancewindings i4 and 20. -A stream oi magnesium vapor is then introducedthrough the inlet i2. Most of the vapor is condensed in'the lower zone Ato a liquid metal, which flows down the walls of the condenser into thereservoir I3. vapor rises into the upper cooler condensing zone B whereit deposits on the walls as a fine duct, some of which falls back intothe pool of molten magnesium in the reservoir I3. Much of the magnesiumdust being condensed clings to the wall of the condensing zone B,forming a deposit which increases in thickness and gradually lowers therate of condensation in the zone. The deposit may be removed from timeto time as necessary by passing electric current through the upperresistance winding 2i, thus heating the walls of the zone B suflicientlyto permit melting of the dust particles nearest the wall, causing thesolid metal deposit to slide down the condenser into the reservoir i3.The dust, on reaching the reservoir fuses and coalesees satisiactorilywith the main body of molten metal. Substantially all the magnesiumvapor entering the condenser is recovered in liquid form, and may betapped oii as desired through the double valves i5 and it. Any fixedgases present in the entering magnesium vapor escape through th upperoutlet is, to which suction may be ap plied ii vacuum operation isdesired.

In an alternative form of the apparatus shown in Figure 2, the magnesiumdust depositing on the wall of the upper condensing zone B iscontinuously removed from the wall by means of a scraper 23 secured to areciprocable shaft 24 The remainin mounted through the cover i8, andfalls into the reservoir i3. In this case, an upper heating elementadapted to dislodge the condensed powder is unnecessary.

The process of the invention may advantageously be applied to thecondensation of magnesium vapor at any pressure, with or without thepresence of accompanying gases such as hydrogen, helium, nitrogen,carbon monoxide, or hydrocarbon vapor. such mixtures are formed in theproduction of magnesium by thermal reduction processes, and in thepurification of magnesium metal by distillation. The new method isespecially useful, however, when the magnesium vapor is supplied undersuch conditions of temperature, pressure, or dilution that the vaporpressure of the liquid magnesium in the condenser, even at itssolidification temperature, is an appreciable fraction, say 3 per centor more,

of the pressure or partial pressure of magnesium in the vapor or vapormixture to be condensed. It is under these conditions, especially when avapor mixture is supplied at an absolute pressure below 100 mm. ofmercury, that dust formation lsmost serious.

In practice the lower or liquid condensing zone A is maintained at anysuitable condensing temperature above the melting point of magnesium(650 (3.), usually in the range 660 C. to 750 C.

The upper or solid condensing zone Bis held preferably at a temperaturesuificiently below the freezing point of -magnesium that the vaporpressure of the solid condensed metal is negligible, temperatures of 50C. to 500 C. being usual, and below 300 C. preferable.

It is not essential to the invention in the broadest form that the solidcondensed magnesium dust be combined with the liquid condensate. Evenwhen the two portions are separately withdrawn from the condenser, therecovery of magneslum is still higher than that attained in ordinarycondensers. However, return of the solid dust to the liquid condense eis a very great advantage, since it permits recovery of substantiallyall of the condensate in the liquid state.

It is to be understood that the foregoing descrlption is illustrativerather than strictly limitative, and that the invention is co-extensivein scope with the following claims.

I claim as my invention:

1. A method of condensing magnesium vapor which comprises passing thevapor successively into two condensation zones maintained atcondensation temperatures respectively above and below the meltingtemperature of magnesium, whereby the major portion of the vapor iscondensed in the first zone directly to a liquid and the remaining vaporis condensed in the second zone as a solid, and combining the condensatefrom the second zone with that formed in the first zone, wherebysubstantially all the magnesium condensed is recovered in the liquidstate.

2. In a method of condensing magnesium vapor wherein the vapor issupplied under such conditions oi temperature and pressure that thevapor pressure of the condensed liquid magnesium formed in the processis an appreciable fraction "of the partial pressure of the magnesiumvapor to be condensed, the steps which comprise passing the vaporsuccessively into two condencation zones, the first being maintained ata condensing temperature above the melting temperature of magnesium andthe second maintained at a temperature such that the vapor pressure ofmagnesium at that temperature is negligible, and combining thecondensate from the second zone with that formed in the first zone,whereby substantially all the magnesium condensed is recovered in theliquid state.

3. In a method of condensing magnesium vapor from admixture with fixedgases, the mixture being supplied under such conditions of temperatureand pressure that the vapor pressure of the condensed liquid magnesiumformed in the procass is an appreciable fraction of the partial pressureof the magnesium vapor to be condensed, the steps which comprise passingthe vapor successively into two condensation zones, the first beingmaintained at a condensing temperature above the melting temperature ormagnesium,

and the second maintained at a temperature such that the vapor pressureof magnesium at that temperature is negligible, and combining thecondensate from the second zone with that formed in the first zone,whereby substantially all the magnesium condensed is recovered in theliquid s to.

4. A method of condensing magnesium vapor from admixture with fixedgases, the mixture being supplied at an absolute pressure below 100 mm.of mercury, which comprises passing the mixture successively into twocondensation Zones.

the first being maintained at a temperature between about 660 C. andabout 750 C., and the second at a temperature between about 50 C. andabout 500 0., and combining the condensate from the second zone withthat formed in the first zone, whereby substantially all the magnesiumcondensed is recovered in the liquid state.

5. In a method of condensing magnesium vapor, the steps which comprisepassing the vapor successively into two condensation zones, the firstbeing maintained at a temperature between about 660 and about 750 C. andthe second at a temperature between about 50 and about 500 C.,

whereby the major portion of the vapor is condensed in the first zonedirectly to a liquid and the remaining vapor is condensed in the secondzone as a solid, and combining the condensate from the second zone withthat from the first zone, whereby substantially all of the magnesiumcondensed is recovered in the liquid state.

JOSEPH D. HANAWALT.

